GMC 2007 Sierra - Manual (Page 155)

{ CAUTION:
Shifting the transfer case to NEUTRAL
can cause your vehicle to roll even if the
transmission is in PARK (P), or if you
have a manual transmission, even if you
are in gear. You or someone else could be
seriously injured. Be sure to set the
parking brake before placing the transfer
case in NEUTRAL. See Parking Brake on
page 169.
N (Neutral): Shift to this setting only when your
vehicle needs to be towed. See Recreational
Vehicle Towing on page 424 or Towing Your
Vehicle on page 423.
2H (Two-Wheel Drive High): This setting is used
for driving in most street and highway situations.
The front axle is not engaged in two-wheel
drive. This setting also provides the best fuel
economy.
4H (Four-Wheel Drive High): Use this setting
when you need extra traction, such as on snowy or
icy roads or in most off-road situations. This
setting also engages the front axle to help drive
your vehicle. This is the best setting to use
when plowing snow.
You can shift from 2H to 4H or 4H to 2H while the
vehicle is moving. The front axle will engage
faster if you take your foot off of the accelerator
for a couple of seconds after you shift. In
extremely cold weather, it may be necessary to
stop or slow the vehicle to shift into 4H.
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